In the area of tire manufacturing, tires are typically made from single or multiple carcasses of substantially U-shaped sections having metal beads at the inner perimeters of the walls. Support can be provided to a tire carcass by steel cord belt plies extending around the outer periphery of the carcass and across the width of the tread. Such steel belt plies are relatively inextensible in the intended direction of rotation of the tire and include steel belt cords disposed parallel to that direction or at a low angle thereto. The belt plies act to restrict the movement of the tread and give the tire better road-holding properties. Support such as this type is particularly important in a radial tire, where the carcass is formed from a rubberized woven fabric having relatively inextensible reinforcing cords running transversely, i.e. radially, from bead to bead.
Technical difficulties have been encountered in incorporating steel belts into the tread area of the tire. One of the difficulties lies in ensuring good adhesion between the steel and the rubber. The centrifugal force of the steel belts can cause difficulty in the adhesion of the belt within the tire. Additionally, movement of the steel belts at higher speeds tends to create excessive temperatures in the tire, which can cause tread failure and de-lamination of the layers comprising the tire. The problem of de lamination is particularly noticeable in the shoulder area of the tire.
One solution of the problem previously used by tire manufactures is to use a layer of calendared fabric laid circumferentially over the belt. This calendared fabric can also be used with wide fabric strips placed over the shoulder area of the tire, retaining the edges of the steel belt in a specific location of the tire. An example of this type of tire can be found in U.S. Pat. No. 4,284,117, issued to Poque et al. on 18 Aug. 1981. In order to cover the entire circumference of the tire and be retained in place, the prior art fabric must overlap itself across the width of tire at some location on the circumference. The overlapping area helps retain the prior art fabric around the circumference of the tire. However, because this type of overlapping adds weight, the potential length of the overlap is limited. A shorter overlap limits the length of the fabric and thereby the strength that the fabric can give to the tire. Additionally, the overlapping section of the fabric causes an uneven thickness of the fabric around the circumference.
To overcome this difficulty, a rubber tape was formed that had cords disposed longitudinally within the tape, and was wound around the belt plies and across the width of the tire. An example of this type of tire can be found in WO 2005/002883, filed by Pirelli Pneumatic S.P.A., and published on 13 Jan. 2005. The continuous nature of the tape provided greater strength. However, the longitudinal yarns were positioned in a spaced apart relationship by the rubber of the tape, which does not provide resistance to the separation of the yarns by items that probe at the area between the yarns.
Additional technical issues are encountered during the tire manufacturing process due to the fact that the tire itself is comprised of many separate layers that are stacked or layered on top of one another until the final vulcanization step, which physically adheres all of the layers together into the final tire product. As these layers are added to form the tire, they have the ability to undesirably shift and move. As a result, when the tire approaches the final step of vulcanization, they layers may be out of place and could result in improperly formed tire products. Due to the seriousness of forming a good, quality tire, this issue of shifting and movement of the layers needs to be minimized as much as possible. The present invention provides a solution to obviate or mitigate these difficulties of the prior art.
The tacky finish of the present disclosure is well suited for providing adherence and stability to several layers of the tire carcass. The tacky finish adheres the textile cap ply layer of the tire to the outer tread layer and to the inner belt ply layer, thus, preventing these layers from moving and/or shifting during the tire manufacturing process. The tacky finish provides these features without interfering with the final vulcanization of the layers of the tire. Furthermore, the tacky finish is temperature and humidity stable, providing adequate product shelf-life that makes it suitable for use end-use products after some aging has occurred.
The inclusion of textile materials coated with the tacky finish of the present invention also allows for a reduction in the amount of other materials needed in formation of the tire. For example, the need for additional rubber coatings may be reduced or eliminated altogether because these rubber coating layers are no longer needed to help improve the adherence of layers of the tire together. Furthermore, the addition of a tacky finish, or textile materials containing the tacky finish, also results in the elimination of some processes normally needed to form the tire. For example, at least one textile component of the tire currently requires exposure to a calendaring process, in order to make it suitable for use in the tire. By incorporating a textile material having a tacky finish thereon, the need for the calendaring process can be eliminated, resulting in reduced complexity in the process of manufacturing tires. For these reasons, and others that will be described herein, the present tack finish represents a useful advance over the prior art.